1. Field of the Invention
The present invention relates to an over-head cam type V-type engine, and more particularly to a V-twin engine comprising a lubricating oil feedback path from the head portion of a cylinder to an oil sump.
2. Description of the Related Art
FIG. 7 is a sectional view showing the structure of a conventional over-head cam type engine for an all terrain vehicle.
As shown in FIG. 7, the engine has a crank case 101 and a crank chamber 101a is formed in the crank case 101. A cylinder 102 is provided to extend upward from the upper end of the crank case 101 such that an inner portion thereof communicates with the crank chamber 101a. Moreover, a crank shaft 103 is provided to penetrate through the crank chamber 101a in a horizontal direction and a piston 104 which reciprocates in the cylinder 102 is coupled through a connecting rod to a portion of the crank shaft 103 which is accommodated in the crank chamber 101a. On the other hand, a head portion 102a of the cylinder 102 is provided with a cam shaft 105 for driving an intake valve and an exhaust valve (not shown) through a cam (not shown). A cam chain 108 for transmitting the rotation of the crank shaft 103 to the cam shaft 105 and rotating the cam shaft 105 is co-wound on sprockets 107 and 106 provided on one end of the cam shaft 105 and a portion 103a of the crank shaft 103 which protrudes toward the outside of the crank chamber 101a, respectively. The cam chain 108 is accommodated in a cam chain tunnel 109 formed in the side portion of the cylinder 102 and a chain chamber 101b formed in the side portion of the crank case 101 to be connected to the cam chain tunnel 109 and separated from the crank chamber 101a through a wall. An oil chamber (not shown) is formed in the crank case 101 to communicate with the lower ends of the chain chamber 101b and the crank chamber 101a. An oil pump and an oil passage (not shown) are provided to supply a lubricating oil accumulated in the oil chamber to the cam shaft 105 provided in the head portion 102a of the cylinder 102 and the like. The reference numeral 110 denotes a belt converter provided on an end of the crank shaft 103 which penetrates through the chain chamber 101b and extends toward the outside thereof. The belt converter 110 serves to cause a driver to easily carry out a speed change operation of a vehicle.
In the over-head cam engine having such a structure, the cam shaft 105 or the like is lubricated by the lubricating oil supplied to the head portion 102a of the cylinder 102 and the lubricating oil which completes the lubrication is returned to the oil chamber through the chain tunnel 109 and the chain chamber 101b. Consequently, the cam shaft 105 or the like is forcibly lubricated.
If the cam shaft structure of the conventional over-head cam engine is to be applied to a engine having two cylinders inclined in opposite directions to each other, it is necessary to provide two sprockets for driving the cam shafts of the two cylinders on the crank shaft. Correspondingly, the length of the crank shaft is increased so that the width of the engine is made greater. There is a cam shaft driving structure in which the cam shafts of the two cylinders are driven through an intermediate shaft by a crank shaft. In such a cam shaft driving structure, the intermediate shaft is provided above the crank shaft to penetrate through the crank chamber and a sprocket for driving the cam shaft of each cylinder is provided in each of portions of the intermediate shaft which protrude toward outsides of the crank chamber, respectively, and only one sprocket for driving the intermediate shaft is provided on the crank shaft. As a result, one sprocket on the crank shaft is omitted, so that the width of the engine can be reduced.
In the cam shaft driving structure, however, if an oil passage extending from the chain chamber to the oil chamber is provided as in the conventional over-head cam type engine, the oil passage is to be formed in both side portions of the crank chamber. For this reason, the size of a crank case is increased, and furthermore, the size of an engine is increased. Moreover, a space in the crank case cannot be utilized effectively.
In order to solve the above-mentioned problems, it is an object of the present invention to provide an over-head cam type V-type engine which can be small-sized and can efficiently utilize a space in a crank case.
In order to attain the object, the present invention provides an over-head cam type V-type engine comprising a crank case having a crank chamber, a crank shaft provided to penetrate through the crank chamber, a first cylinder and a second cylinder provided in an upper portion of the crank chamber to be positioned on virtual lines extending like a V-shape upward from a center of the crank shaft as seen in an axial direction of the crank shaft, respectively, a cam shaft provided in a head portion of each of the first and second cylinders, an intermediate shaft provided above the crank shaft to penetrate through the crank chamber, a first transmitting means for transmitting a rotation of the crank shaft to the intermediate shaft through a chain at one of end sides of the intermediate shaft, a chain chamber formed adjacently to a side portion of the crank chamber and serving to accommodate the first transmitting means, a second transmitting means for transmitting a rotation of the intermediate shaft to the cam shaft of one of the first and second cylinders through a chain at the other end side of the intermediate shaft, a first chain tunnel for accommodating the second transmitting means, a third transmitting means for transmitting the rotation of the intermediate shaft to the cam shaft of the other cylinder through a chain at one of the end sides of the intermediate shaft, a second chain tunnel for accommodating the third transmitting means, an oil sump formed in a lower portion of the crank case and serving to accumulate a lubricating oil therein, a forcible oil supply means for supplying the lubricating oil from the oil sump to the head portion of each of the first and second cylinders such that each cam shaft is lubricated, a first lubricating oil feedback path formed such that the lubricating oil supplied to the head portion of one of the first and second cylinders flows down into the oil sump through the first chain tunnel and the crank chamber, and a second lubricating oil feedback path formed such that the lubricating oil supplied to the head portion of the other cylinder flows down into the oil sump through the second chain tunnel and the chain chamber.
In this specification, xe2x80x9cabovexe2x80x9d also implies an obliquely upward direction as well as a just upward direction.
According to such a structure, the lubricating oil feedback path utilizes the inner space of the crank chamber, so that a space in the crank case can be saved. Consequently, the space of the crank case can be utilized efficiently. Moreover, the size of the engine can be reduced.
The cylinder may have a skirt portion, the skirt portion being provided to be inserted into the crank chamber, and an inlet hole for the lubricating oil flowing from the first chain tunnel into the crank chamber may be opened in a portion of an internal surface of the crank chamber which is opposed to a peripheral surface of the skirt portion of the cylinder.
According to such a structure, even if the lubricating oil vigorously flows into the crank chamber through the inlet hole, it hits against the skirt portion of the cylinder and is thereby prevented from advancing toward the inside of the crank chamber. Consequently, it is possible to prevent the lubricating oil from splashing on the crank shaft positioned in the crank chamber and its temperature from being raised.
A lubricating oil guide member may be provided on the internal surface of the crank chamber to guide the lubricating oil flowing into the crank chamber from the first chain tunnel through the inlet hole for the lubricating oil toward the oil sump avoiding a rotation region of the crank shaft accommodated in the crank chamber.
According to such a structure, the lubricating oil flowing from the inlet hole can be guided toward the oil sump so as not to splash on a crank web or a crank pin. As a result, it is possible to more effectively prevent the temperature of the lubricating oil from being raised.
The lubricating oil member may extend between an inner side surface of the crank chamber and an outer surface of the skirt portion of the cylinder circumferentially outside of rotation region of crank shaft from lower end of the inlet hole.
The first chain tunnel may be formed to extend from the head portion of one of the first and second cylinders and terminated in a portion of the crank case which includes the other end of the intermediate shaft, a belt converter for transmitting a power of the V-type engine to a transmission may be provided adjacently to the crank chamber in a portion of the crank shaft which protrudes from the crank chamber toward the other end side of the intermediate shaft, and an ambient air intake passage for cooling the belt converter may be formed adjacently to a terminating portion of the first chain tunnel.
According to such a structure, the size of the ambient air intake passage for cooling the belt converter can be reduced by effectively utilizing a space in the crank case. Furthermore, the amount of the protrusion of the belt converter toward the side can be decreased. Consequently, the width of the engine can be reduced.
The ambient air intake passage may be provided under the first chain tunnel and around a support boss which has a bearing supporting the crank shaft therein and protrudes from a side wall of the crank chamber.
These objects as well as other objects, features and advantages of the present invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.